1. Field of the Invention
This invention relates to the traffic load regulation on fixed stations, also referred to as relays, in a cellular radio communications network. Consequently this regulation conditions the selection of a fixed station by a mobile station.
2. State of the Prior Art
A radio communication system typically comprises the following members:
Mobile stations which include in particular a radio transmitter/receiver (transceiver), select one of the radio relays as soon as powered up, exchange digital data with the relay, select a radio channel of this relay, set up and receive outgoing and incoming telephone communications via the relay; and
A fixed communication network consisting of:
fixed radio stations (base stations), which each manage a set of radio channels, including one or several signalling radio channels, to exchange digital data with the mobile stations, and interface protocols to set up communications between the telephone network and the mobile stations; and PA1 an infrastructure comprising computers, switches, and means for carrying digital data and telephone signals thereby implementing functions of switching, location of mobile stations in the network, operating, and optimization of the traffic load in the network. PA1 computing a field correction parameter as a function of at least on a load indication of the fixed station depending on the traffic passing over the fixed station and periodically re-evaluated, and on fixed factors, PA1 transmitting the field correction parameter to the mobile stations, and PA1 correcting the measured radio-electric field corresponding to the fixed station by the correction parameter into a corrected field in each of the mobile stations, so that the mobile station compares the corrected fields corresponding to the fixed stations and selects one of the fixed stations corresponding to the highest corrected field to establish a radio communication with the selected fixed station.
The most recent heavy traffic networks consist of a large number of fixed stations, each fixed station covering a small geographical area. The radio-electric coverage of a fixed station is then referred to as "cell" and the network is qualified as "cellular".
As the radio-electric resources are limited, it is particularly of interest to manage the network so as to distribute the traffic load between the radio channels and hence between the fixed stations.
In the most recent cellular radiotelephone systems, such as the RADIOCOM 2000 system and Pan-European GSM system, certain means are scheduled to act on the radio load. They can be classified into the following categories:
When a relay has its traffic saturated, it broadcasts saturation data generally in binary, that forbids or strongly dissuades the mobile stations from selecting this relay. Sending of the data is automatically triggered by the fixed station or by the infrastructure in the events of a serious disturbance in the operation. This type of means cannot be used to obtain effective optimization of the radio load.
The cellular networks offer the function of cell transfer in the mobile station whereby a communication in progress continues without interruption when the mobile station moves from one cell to another. In certain systems it is scheduled that in the event of a large scale load on a fixed station the mobile station can be transferred to another cell at the time of setting up the communication or during the communication. In fact it is observed that the greater part of the load on the radio-electric channels is due to telephone communications.
This second solution offers the following drawbacks:
Complexity: the process of cell transfer decision in the mobile station takes account of a large number of parameters including radio-electric measurements made in the adjacent relays and the degree of saturation of these relays. This is a real time process which should be brief, a few seconds. This mechanism is therefore difficult to obtain and to optimize.
Reduction in the quality of the communication: any transfer of mobile station very frequently results in an audible reduction, or a delay in the setting up of the communication.